Circuit and method for activating an nfc device

ABSTRACT

An embodiment near-field communication (NFC) router, includes a first switch coupled between a first terminal of the NFC router and a second terminal of the NFC router; and a rectifier bridge having an output terminal coupled to a control terminal of the first switch, the rectifier bridge being configured to rectify a signal detected by an antenna external to the NFC router.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/702,105, filed Sep. 12, 2017, which application claims priority toFrench Patent Application No. 1751184, filed on Feb. 14, 2017, whichapplications are hereby incorporated herein by reference.

TECHNICAL FIELD

The present description generally relates to electronic circuits andmobile communication equipment and, in particular embodiments, a circuitand a method for activating a near-field communication (NFC) device.

BACKGROUND

Many devices are now provided with near-field communication functions.The most widespread are mobile telecommunication devices (e.g., mobilephones or smartphones) which are increasingly often provided with anear-field communication interface, generally referred to as an NFCrouter, conferring additional functionalities on the phone. NFC routersenable a mobile device to operate either in card mode, the device thenhaving the functions of a contactless communication card, or in readermode, the device then having the functions of a contactless card readingand/or writing terminal.

Whether in card mode or in reader mode, the NFC router is powered by thebattery of the device that contains the router. The battery of thedevice itself is generally charged by being connected, via a charger,to, e.g., the electrical distribution network, dynamo, solar panel, etc.

SUMMARY

Embodiments of the invention remedy all or part of the drawbacks of thedevices combining battery and near-field communication interface.

Embodiments of the invention improve the energy management of such adevice.

Embodiments of the invention provide a solution particularly suited todevices operating only in card mode or in peer-to-peer card mode.

An embodiment provides a near-field communication router includes afirst switch internal to the router and between a first terminal of therouter and a second terminal of the router. A control terminal of thefirst switch is linked to an output terminal of a rectifier bridge forrectifying a signal picked up by an antenna external to the router.

According to an embodiment, the control terminal of the first switch islinked to the output terminal of the rectifier bridge by a resistive andcapacitive cell.

According to an embodiment, the cell includes a resistive elementconnecting the output terminal of the rectifier bridge to the controlterminal of the first switch and a capacitive element connecting thecontrol terminal of the first switch to the second terminal of therouter.

An embodiment provides a system for activating a near-fieldcommunication router includes a first switch internal to the router andbetween a first terminal of the router and a second terminal of therouter. A control terminal of the first switch is linked to an outputterminal of a rectifier bridge for rectifying a signal picked up by anantenna. A second switch is external to the router and located between afirst terminal for applying a voltage supplied by a battery and a thirdterminal of the router. A control terminal of the second switch isconnected to the first terminal of the router.

According an embodiment, the first terminal of the router is linked, bya resistive element external to the router, to the first terminal forapplying a voltage supplied by a battery.

According to an embodiment, the third terminal of the router isconnected to the earth.

An embodiment provides a portable communication device including arouter as described.

An embodiment provides a portable communication device including asystem as described.

An embodiment provides a method for activating a contactlesscommunication router. The presence of a voltage is detected at theterminals of a rectifier bridge for rectifying a signal picked up by anantenna while no voltage is applied between the power supply terminalsof the router. A power supply voltage is applied between the terminals.

BRIEF DESCRIPTION OF THE DRAWINGS

These features and advantages, as well as others, will be disclosed indetail in the following non-restrictive description of particularembodiments in relation to the accompanying figures in which:

FIG. 1 is a partial, schematic block diagram of an example of anelectronic device of the type to which the embodiments that will bedescribed apply;

FIG. 2 is a simplified, partial diagram of an embodiment of an NFCrouter; and

FIG. 3 schematically illustrates the trigger circuit operation fortriggering the power supply of an NFC router.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The same elements have been designated by the same references in thedifferent figures.

For the sake of clarity, only the steps and elements useful to theunderstanding of the embodiments that will be described have beenrepresented and will be given in detail. In particular, the operation ofa near-field communication router has not been given in detail, theembodiments described being compatible with common operation. Inaddition, the applications of a device or system incorporating such arouter have also not been given in detail, the embodiments describedbeing, once again, compatible with common applications.

Unless specified otherwise, when reference is made to two interconnectedelements, this means directly connected without any intermediate elementother than conductors, and when reference is made to two interlinkedelements, this means that these two elements may be directly linked(connected) or linked via one or more other elements.

In the description that follows, when reference is made to the termsapproximately, about and in the order of, this means within 10%,preferably within 5%.

FIG. 1 is a schematic representation in the form of blocks of anear-field communication system partially illustrating an embodiment ofa mobile device 1 provided with a battery and a near-field communicationcircuit.

In some embodiments, the present description applies more particularlyto devices including a near-field communication circuit and arechargeable battery.

The device 1 includes, inter alia, a near-field communication interface2 (also referred to herein as NFC router 2) connected to an antenna 14for communicating with a terminal 3 when the device 1 is a shortdistance from the terminal 3. The device 1 further includes a battery 16for operating this device regardless of the near-field communicationmode. For example, in the case of a mobile phone, the battery 16 makesit possible to operate the phone for GSM-type telecommunication. Thebattery 16 is charged by a charger 18 provided in the device 1 andgenerally receiving a DC voltage from a terminal 182 intended to beconnected to an external transformer. The battery 16 also powers the NFCrouter 2, whether in reader mode, in card mode, or in peer-to-peer mode.

The device 1 further includes various processing circuits according toits nature. These circuits have been symbolized in FIG. 1 by a processor13. These circuits are capable of being powered by the battery 16 and,at least for some of them, communicating with the NFC router 2.

The battery charger 18 is generally a voltage regulation system forproviding the battery 16 with a suitable charge voltage and monitoringthe battery charge.

In a “peer-to-peer” or P2P operating mode, two devices provided with NFCrouters 2 communicate with each other for exchanging information. Insuch an operating mode, each device operates alternately in card modeand in reader mode.

When an NFC device (notably a portable device) operates in reader orterminal mode, its battery powers the NFC router 2 and the processingcircuits 13.

However, in periods of standby or non-operation of the NFC router, it isplaced in a low consumption mode.

A common solution for avoiding power consumption by the router 2 even instandby mode, is that the NFC router 2 is not powered during standbyperiods and that the user activates a switch (e.g., the standby switch)to switch it back on. However, this requires an intervention by theuser.

Another solution would be to leave the circuits of the NFC router 2active (powered). However, this is incompatible with the desire forminimum power consumption in standby mode.

FIG. 2 is a simplified, partial diagram of an embodiment of an NFCrouter 2.

This router 2 includes two terminals 22 and 24 to which the antennacircuit 14 is connected. This circuit 14 includes a parallel oscillatingcircuit formed of an inductive element 142 forming the antenna and acapacitive element 144 in parallel (or in series in other embodiments).In some cases, the capacitive element 144 is incorporated in the router2. One or both terminals 22 and 24 are linked to the near-field circuits28 and other circuits of the router 2 in order to convey the signals(received and transmitted) of the communication (the signals whichcontain the modulation carrying the information). These circuits 28 aregenerally the radio frequency encoding and decoding circuits as well asthe various NFC processing circuits.

The circuits 28 are intended to be powered by the battery 16. To do so,a terminal 27 of the router 2 is linked to a terminal 17 linked to thebattery 16, more precisely to the positive terminal of the battery,supplying a potential VBAT.

According to the embodiment represented, the two terminals 22 and 24 arelinked to the respective anodes of two rectifying elements (preferablytwo diodes 262 and 264) mounted in a bridge 26, the cathodes of whichare interconnected (e.g., form a node) at a terminal 23.

Today, either the battery continuously powers at least a standby mode ofthe circuits 28, which then includes, where appropriate, elements fordetecting the presence of a field picked up by the antenna 14 in orderto wake up the other elements, or a switch triggered by an action of theuser is provided between the battery 16 and the terminal 27. In thefirst case, there is pointless residual consumption. In the second case,operation is impractical and activation takes time.

According to the embodiment represented in FIG. 2, a switch 42, e.g., ap-channel MOS transistor, is inserted between the terminals 17 and 27.This switch 42 is therefore external to the router 2. The controlterminal 421 (e.g., gate) of the switch 42 is linked to a terminal 29 ofthe router 2. The terminal 29 is linked to the terminal 17 via aresistive element 44. Inside the router 2, the terminal 29 is linked, bya switch 46, e.g., an n-channel MOS transistor, to the earth) or ground)connection terminal 25. The control terminal (e.g., gate) of thetransistor 46 is linked by a resistive and capacitive cell 48, includinga low-pass filter, to the output 23 of the rectifier bridge. The cell 48includes a resistive element 482 connecting the terminal 23 to the gateof the transistor 46 and a capacitive element 484 linking the gate ofthe transistor 46 to the terminal 25 (the earth). The time constant ofthe cell 48 is selected according to the operating frequency of the NFCantenna 14, typically 13.56 MHz in order to smooth the signal rectifiedby the bridge 26 and control the transistor 46.

The role of the transistor 46 is to cause the closure of the transistor42 when a radio frequency radiation in the NFC range of frequencies ispicked up by the antenna 14.

The transistors 42 and 46, with the resistive element 44 and the filter48, constitute a trigger circuit for triggering the power supply of therouter 2 by the battery 16.

Other embodiments of this trigger circuit using passive components,except for the switch 46, are conceivable. Indeed, other passivecircuits for detecting the field at the terminals of the antenna may beprovided which are capable of activating the transistor 46.

FIG. 3 very schematically illustrates the trigger circuit's operation.This figure represents simplified examples of progressions of the gatevoltage VG46 of the transistor 46, the gate voltage V421 of thetransistor 42 and the voltage V27 of the terminal 27.

For simplifying the representation of the figures, parasitic voltagedrops are not taken into account and the voltage levels are symbolizedby levels 0 and 1.

In the absence of any radio frequency field (indicated as NO FIELD inFIG. 3) picked up by the antenna 14, the gate of the transistor is notpolarized (voltage VG46 at zero) and the transistor 46 is blocked.Consequently, the gate of the transistor 42 is in a high state (voltageVG421 at the level VBAT) and the transistor 42 is also blocked. Theterminal 27 is not powered (level zero).

In this operating mode, the router 2 is not powered. The onlyconsumption of the router 2 comes from the losses in the transistor 46in the blocked state and is therefore minimized.

In the presence of a field (indicated as FIELD in FIG. 3) picked up bythe antenna 14, the gate signal VG46 of the transistor 46 switches tothe high state. The level depends on the voltage recovered at theterminals of the resonant circuit of the antenna 14. The switching ofthe transistor 46 takes place (time t) as soon as this rectified andfiltered level reaches the threshold voltage of the transistor 46. Theconduction of the transistor 46 causes the drop in the gate voltage V421of the transistor 42. The low level VL of the voltage V421 correspondsto VBAT*(R44+R46)/(R44*R46), where R44 represents the value of theresistive element 44 and R46 the drain-source resistance of thetransistor 46 in the “on” state. The low level VL is below the thresholdvoltage Vth42 of the transistor 42, which causes its closure orconduction. This causes the powering of the router 2 from the terminal27 which receives the voltage VBAT reduced by the drain-source voltagein the “on” state V42 of the transistor 42.

In this operating mode, the consumption of the router 2 is increased bydissipation in the drain-source resistances in the “on” state of thetransistors 42 and 46. However, this is in an out-of-standby mode inwhich such consumption is acceptable.

One advantage of the embodiments described is that the consumption ofthe router in standby mode is minimized while allowing an automatic exitfrom the standby mode in the presence of an NFC field.

One advantage of the embodiments described is that they are compatiblewith a deactivation of the router by the current solutions, e.g., by theprocessor of the phone for deactivating the function. For example, theterminal 17 is then linked to the battery (or to a power supply railfrom the battery) by a switch controlled by the processor.

According to another example, provision is made to connect the terminal29 to an output terminal of the processor for forcing a drop in thepotential of the gate of the transistor 42 when it is wanted to triggerthe power supply of the router 2 regardless of the presence of a field.

Another advantage of the embodiments described is the small number ofadded components (two external to the router, three internal to therouter).

Various embodiments have been described, various variants andmodifications will be apparent to the person skilled in the art. Inparticular, the practical implementation of the embodiments and thedimensioning of the components (resistors 44 and 482, capacitor 484 andtransistors 42 and 46) is within the grasp of the person skilled in theart from the functional description given above.

What is claimed is:
 1. A near-field communication (NFC) router,comprising: a first terminal; a second terminal; a third terminalconfigured to be coupled to a voltage source through a first switch thatis external to the NFC router; a rectifier bridge having input terminalscoupled to terminals of an antenna external to the NFC router, therectifier bridge being configured to rectify a signal detected by theantenna external to the NFC router; and a trigger circuit, comprising: asecond switch internal to the NFC router and coupled between the firstterminal of the NFC router and the second terminal of the NFC router;and a filter comprising a resistive element having a first terminal anda second terminal, the first terminal of the resistive element beingcoupled to form a node with an output terminal of the rectifier bridge,the second terminal of the resistive element being coupled to form anode with a control terminal of the second switch, wherein the firstswitch comprises a first transistor of a first conductivity type, andwherein the second switch comprises a second transistor of a secondconductivity type different from the first conductivity type.
 2. The NFCrouter according to claim 1, wherein the first terminal of the NFCrouter is further coupled to the voltage source.
 3. The NFC routeraccording to claim 2, wherein the first terminal of the NFC router isfurther coupled to the voltage source through a second resistive elementthat is external to the NFC router.
 4. The NFC router according to claim1, wherein the filter further comprises: a capacitive element coupledbetween the control terminal of the second switch to the second terminalof the NFC router.
 5. The NFC router according to claim 1, furthercomprising communications circuitry coupled to the third terminal, thecommunications circuitry being configured to be powered by the voltagesource via the third terminal.
 6. The NFC router according to claim 1,wherein the third terminal is configured to be coupled to the voltagesource through a current path of the first transistor, and wherein thefirst terminal of the NFC router is configured to be coupled to acontrol terminal of the first transistor.
 7. The NFC router according toclaim 1, wherein the second terminal of the NFC router is configured tobe coupled to a reference potential.
 8. The NFC router according toclaim 7, wherein the reference potential comprises a ground potential.9. A system, comprising: a near-field communication (NFC) router,comprising: a first terminal configured to be coupled to a battery by afirst electrical path; a second terminal configured to be coupled to areference potential; a third terminal configured to be coupled to thebattery by a second electrical path different from the first electricalpath; a rectifying circuit configured to rectify a signal detected by anantenna; and a trigger circuit, comprising: a first switch coupledbetween the first terminal and the second terminal; and a firstresistive element having a first terminal and a second terminal, thefirst terminal of the first resistive element being coupled to form anode with an output terminal of the rectifying circuit, the secondterminal of the first resistive element being coupled to form a nodewith a control terminal of the first switch; and a second switchexternal to the NFC router and coupled along the second electrical pathbetween the battery and the third terminal of the NFC router, wherein acontrol terminal of the second switch is coupled to the first terminalof the NFC router.
 10. The system according claim 9, further comprisinga second resistive element along the first electrical path, wherein thesecond resistive element is coupled between the first terminal of theNFC router and the battery.
 11. The system according to claim 9, whereinthe rectifying circuit comprises: a first diode having an anode coupledto a fourth terminal of the NFC router, and a cathode coupled to theoutput terminal of the rectifying circuit; and a second diode having ananode coupled to a fifth terminal of the NFC router, and a cathodecoupled to the output terminal of the rectifying circuit.
 12. The systemaccording to claim 11, further comprising the antenna having terminalscoupled to the fourth terminal of the NFC router and the fifth terminalof the NFC router.
 13. The system according to claim 9, wherein thefirst switch and the second switch comprise transistors of oppositeconductivity types.
 14. The system according to claim 9, wherein the NFCrouter further comprises a capacitive element coupled between thecontrol terminal of the first switch and the second terminal of the NFCrouter.
 15. The system according to claim 9, wherein the systemcomprises a portable communication device.
 16. A method for activating acontactless communication router, the method comprising: decoupling afirst terminal of the contactless communication router from a secondterminal of the contactless communication router in response to nosignal being detected by an antenna, the first terminal of thecontactless communication router being controllably coupled to areference potential via a first switch coupled between the firstterminal and the second terminal of the contactless communicationrouter, the second terminal of the contactless communication routerbeing tied to the reference potential; decoupling a third terminal ofthe contactless communication router from a power supply voltage inresponse to no signal being detected by the antenna via a second switchcoupled between the third terminal and the power supply voltage, thethird terminal being configured to supply the power supply voltage tocommunication circuitry of the contactless communication router;coupling the first terminal of the contactless communication router tothe reference potential in response to a signal being detected by theantenna; and coupling the third terminal of the contactlesscommunication router to the power supply voltage in response to thecoupling of the first terminal of the contactless communication routerto the reference potential.
 17. The method according to claim 16,wherein the contactless communication router comprises a rectifierbridge, a resistive element, and a first switch, the first switch beingcoupled between the first terminal and the second terminal of thecontactless communication router, the rectifier bridge being coupledbetween the antenna and a first terminal of a resistive element, thesecond terminal of the resistive element being coupled to form a nodewith a control terminal of the first switch, and wherein coupling thefirst terminal of the contactless communication router to the referencepotential in response to the signal being detected by the antennacomprises: generating, by the rectifier bridge, a control signal inresponse to the signal being detected by the antenna; and triggering thefirst switch from an open state to a closed state using the controlsignal.
 18. The method according to claim 17, wherein coupling the thirdterminal of the contactless communication router to the power supplyvoltage in response to the coupling of the first terminal of thecontactless communication router to the reference potential comprises:triggering the second switch from an open state to a closed state inresponse to the first terminal of the contactless communication routerbeing coupled to the reference potential.
 19. The method according toclaim 18, wherein a control terminal of the second switch is coupled tothe first terminal.